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Old September 5th, 2009, 20:33
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Ecomike Ecomike is offline
NAXJA# 2091
 
Join Date: Dec 2006
Location: MilkyWay Galaxy
Posts: 15,358
Re: Renix Cooling Tips

I have done some extensive data collection on the 87-90 cooling systems and found some interesting things. First you need to distinguish between the thermostat housing temperature (180 to 220 F depending on T-stat choice and heat load) which is the maximum coolant temperature and the radiator exit coolant temperature where the Renix ('87-'90 years) XJs TFS is located. When I installed a new aluminum 2 row radiator 4 years ago with a new TFS the fan switch tripped on at a radiator outlet coolant temp of 175 to 180 F and off at 160 -165 F.

Then earlier this summer my jeep was overheating long before the TFS got hot enough to turn on. The problem turned out to be that the radiator flow was comprimised after just 4 years, and the coolant was flowing slowly through the radiator, getting down to 170 F, not tripping the e-fan, but the coolant was getting way to hot coming out of the engine. I tried a new water pump, new thermostat, hot wired the efan, a new ZJ fan clutch ( basically a HD XJ fan clutch), and a new 3 row copper/brass CSF radiator was the last desperate thing I tried, and only the new radiator solved the problem.

With the 4 year old radiator I had a 40 F delta T across the radiator, which was deceptively looking like a good radiator. Problem is I had no way to measure flow rates. Now the new radiator has only given me a 15 F delta T, but the jeep does not overheat now with the new radiator.

So WTF!

Conterintuitive, but what has happened is the new radiator seems to have 3-4 times the flow rate as the older one, and while the Delta is lower, it is removing more total heat that before (Q= Mass rate times the delta T). Also the exit temperature of the new radiator is hotter than before, so my TFS for the e-fan comes on sooner now (another deceptive surprize to our prior analysis)

Needless to say, this was all a real big surprise to me, and should be to most of us here!!!! I know I had everyone here scratching their head over my recent problem.
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34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091

Last edited by Ecomike; September 5th, 2009 at 20:39.
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